Category Archives: Friday Fellow

Bacteria are found almost everywhere across our planet and they are essential for the survival of every other lifeform, including the fascinating, and for some disgusting, cockroaches. One special cockroach-friendly genus of bacteria has the adequate name Blattabacterium, whose best-known species is Blattabacterium cuenoti, which I decided to call the “common cockroach bacterium”.

This interesting species, like all species of Blattabacterium, is an obligate endosymbiont of cockroaches, meaning that it can only exists inside cockroach cells. More specifically, the common cockroach bacterium lives inside the cells of the fat bodies of cockroaches, i.e., their adipose tissue. It was found living inside all cockroach species examined to date with the exception of the genus Nocticola. It is also found inside the termite Mastotermes darwinensis because, if you did not know yet, termites are nothing more than highly specialized cockroaches. Thus, it is thought that this bacterium first “infected” the ancestor of all modern cockroaches about 140 million years ago and has only been lost in two lineages, the one from Nocticola and the one from termites.

Blattabacterium cuenoti cells shown in red (above) and gray (below). The cyan areas in the bottom image represent the nucleus of the cockroach cells. Extracted from Sabree et al. (2009).

Although many cockroaches are generalist feeders, being able to feed on almost everything, the main diet of all species is decaying plant material, and this is a relatively nitrogen-poor food. In order to increase their nitrogen intake, cockroaches store uric acid, a common product of protein metabolism. Most animals, including humans, excrete uric acid in their urine, but cockroaches store it in their adipose tissue. Thus, it was originally thought that the cockroach bacteria, by living close to uric acid reserves in the adipose tissue, could use uric acid directly as a food source, but studies have found this is not the case.

When necessary, cockroaches release this uric acid and it is broken down into urea or ammonia by bacteria living in their guts. After that, the common cockroach bacteria can use those compounds to synthesize glutamate, essential amino acids and vitamins for the cockroach.

Since they cannot use uric acid directly, it is a mystery why the common cockroach bacteria lives so close to the place where this substance is stored. One suggestion is that it was originally able to use uric acid but lost this ability by genome reduction.

The functional gene categories of Blattobacterium are very similar to those of Blochmannia, an endosymbiotic bacterium from carpenter ants, which also feed on plant material. However, Blochmannia is very distantly related to Blattobacterium, suggesting that their similar genomes are the result of convergent evolution caused by similar lifestyles.

The family Asteraceae (or Compositae), sometimes called “the daisy family”, is the largest family of plants, with more than 30 thousand currently accepted species. This family is characterized by a typical inflorescence called capitulum (or head in English), which is formed by several small flowers arranged in a compact form so that the whole structure resembles a single flower. One of its subfamilies, Carduoideae, include species known as thistles and, among them, one genus, Echinops is quite unusual among the whole family.

The heads of Echinops, different from most Asteraceae, contains a single flower, and these single-flowered heads are arranged in secondary inflorescences that form a globose structure, Thus, species of Echinops are named ‘globe thistles’. Most species of globe thistle have blue or white flowers but one species, Echinops amplexicaulis, has a dark red color. Although not having a common name in English as far as I know, I think that ‘red globe thistle’ is an excellent name.

Found in dry grasslands and dry forests in Central Africa, the red globe thistle reaches a height of about 1 to 1.5 m and has a vertical, usually unbranched stem with hardened leafs whose margin is dentate and the lobes have a terminal spine, as typical of thistles.

Specimen in the Democratic Republic of the Congo. Photo by Mathias D’haen.*

The roots of the red globe thistle are traditionally used in Uganda and Ethiopia to treat a series of conditions, including AIDS, trypanosomiasis, ulcerative lymphagitis, hydrocele, tuberculosis and stomachache. Laboratory studies have identified anti-tuberculosis activity of the root extract in vitro against several strains of Mycobacterium, including strains resistant to the currently common drugs used to treat the infection.

Apparently there is no study addressing the other alleged effects of the plant. There are also no studies on the ecology or life cycle of this species. In other words, that’s all I can tell about this lovely and peculiar globe thistle.

The most popular fungi are certainly the gilled mushrooms, many of which are large, fleshy and delicious, or sometimes deadly poisonous. However, there are also some gilled mushrooms that are not that conspicuous and sometimes are not even noticed by most people because of their small and fragile aspect.

If you are walking through the forests of South America, especially the Amazonian and Atlantic forests, and pay enough attention to the leaf litter, you may eventually see a small mushroom pretending to be a dead leaf with its brownish purple hat full of irregular pale yellow spots. Its name is Marasmius amazonicus and, although it lacks a common name, I think that Amazonian parachute would be a reasonable choice.

A polka-dott parachute growing in the Amazonian forest in the state of Mato Grosso, Brazil. Photo by Rich Hoyer.*

The Amazonian parachute belongs to the genus Marasmius, whose species are often called parachutes in English due to their pileus (cap) showing folds caused by the underlying lamellae (gills). When you look it from below, you can notice that the lamellae are thin and apart from each other, letting the pileus visible between them.

A beautiful shot of the same specimen seen above. Photo by Rich Hoyer.*

The word Marasmius comes from Greek μαρασμός (marasmos), meaning withering. The name is adequate to these mushrooms because of their peculiar behavior. While the fruiting bodies of most mushrooms appear at a particular moment and last for a determinate ammount of time before deteriorating, the fruiting bodies of Marasmius can dry out if the humidity levels become too low and later revive when moistened. Their delicate appearance, with thin caps and even thinner stalks, sometimes looking like a hardened hair, makes this process easier.

Being a decomposing species like most species of Marasmius, the Amazonian parachute is found growing on dead plant matter, including rotting branches and leaves. Although its fruiting bodies are able to dry out and revive during dry conditions, they can only grow in environments that have high humidity levels most of the time. Thus, although they can grow on dead leaves, they can only do so after the leaves become more fragmented and compacted against the forest floor in order to retain enough moisture.

The ecology of the Amazonian parachute is basically unknown up to this date, although many can be infered by comparison with other Marasmius species. Is it a poisonous mushroom? Probably not, but it is likely not edible either.

There are more than 3000 species of cicada worldwide and they are often associated with the summer when they become adults and their songs can be heard coming from the trees. Today we will focus on an Australian species, Psaltoda claripennis, known as the clanger cicada.

The clanger cicada is found in eastern Australia and is common around in Brisbane and nearby areas, where it can be easily seen on tree branches, sometimes in groups. They have a brownish dorsum with some dark, sometimes black, segments in the abdomen. The ventral side is pale, except for the abdomen, which is brown, and the legs are yellow. The eyes are light red to brownish red and the wings are transparent with green veins. Males measure about 30 mm in length and females are slightly smaller, about 25 mm long.

I wasn’t able to find much information about its natural history. This species was actually just one more among many cicada species until some years ago when an interesting discovery was made.

Cicada wings are beautiful structures and are usually very clean. In fact, many insect species find ways to maintain their wings clean even in very contaminated environments and one of the reasons for it is that insects wings are extremely hydrophobic, i.e, they repel water just like many plant leaves. Since water has a hard time trying to attach to their wings, microorganisms associated with water cannot get to the wings either.

But the wings of the clanger cicada are more than only hydrophobic. Studies have shown that every cell of gram-negative bacteria that happens to touch the wing surface is deformed and dies. The same did not happen with gram-positive bacteria, though. As the studies progressed, researches started to understand the structural arrangement of the wings. Their surface is formed by very small pillars, only about 30 nm high and distant 170 nm from each other. When a gram-negative bacterium falls on those pillars, its soft membranes start to slide to the space between them and stretch enough to break. The poor cell ends up as a dead disformed mass. Gram-positive bacteria have more rigid cell walls and are resistant to stretch, but treating them with microwave decreased their rigidity and allowed them to be killed as well.

Nanostructure of the clanger cicada’s wing and the representation of how a bacterium dies by touching it. Credits to Pogodin et al. (2013).

Further research on this structure can lead to the development of new materials that remain sterile even after contacting a pathogen.

Once more the diversity of lifeforms brought us ways to improve our society. How many more useful stuff are hidden in the forests and fields? Preserving the ecosystems is the best for every inhabitant of this planet.

Grasses make up one of the most successful families of flowering plants and are the main characters in grasslands, which can cover huge areas of Earth’s surface. Not all species cover large areas, though, at least not in their native habitats. One example is Pennisetum macrourum, the so-called African feather grass.

Native from South Africa and nearby countries, the African feather grass is a perennial species that grows in soils that experience periodic flood. Thus, it usually grows around larger water bodies or in areas that form temporary ponds during the rainy season.

A patch of African feather grass in the Kruger National Park in South Africa with a southern greater kudu (Tragelaphus strepsiceros strepsiceros) in the background. Photo by Johnny Wilson.*

Growing up to 2 m in height, the African feather grass grows in dense patches and does not spread evenly across the substrate. It produces the typical inflorescence of the genus Pennisetum, a narrow and dense panicle with spikelets interspersed with bristles, giving it a fluffy aspect. The fresh panicle is light green to white but turns light brown when ripe.

While most grasses die during the dry season, the African feather grass persists throughout the year, being an important food source for wild grazing animals and is also given as food for domesticated cattle. It is not a very tasteful and nutritious grass, though, and most animals avoid eating it when other grasses are available.

Despite its importance for native species in Africa, the African feather grass has gained the status of a vilain elsewhere. The species was introduced in New Zealand and Australia and became an noxious weed. Spreading quickly throughout the environment, the African feather grass outcompetes native grasses and is not regarded as a high quality food for grazing animals there either. Nevertheless, I was unable to find any recent work addressing this situation, including the current status of this grass in the aforementioned countries and ways to control its spread.

Panicles covered with spider web and dew in New Zealand. Photo by iNaturalist user ben_banks.*

It seems that is still a lot to be studied about this African grass in both its native habitats and places where it was introduced.

Last week I presented a beautiful sea snail, the common sea butterfly, with wing-like parapodia that allows it to swim. The sea butterflies belong to a group of marine gastropods known as Pteropoda due to this foot modified into fins. There are two main groups of pteropods, Thecosomata, that have a shell, and Gymnosomata, that don’t have a shell. While the shelled ones are called sea butterflies, the naked ones are called sea angels or naked sea butterflies.

The most popular sea angel is Clione limacina, the common sea angel. Its body is mostly transparent and, like all pteropods, has two parapodia that look like wings which, together with its elongate and shell-less body makes it look like an angel indeed. Despite its angelic appearance, the common sea angel is a fearsome creature.

Being a predator, the common sea angel is specialized in eating the common sea butterfly. Both species share the same environment in arctic waters and their association is known for centuries. The way that the common sea angel captures and eats the common sea butterfly is impressive and kind of scary.

A specimen, that was washed ashore, on a human hand for comparison. Photo by iNaturalist user nbenson.*

When the sea angel detects a sea butterfly nearby, it starts a pursue and everts six adhesive buccal cones from its mouth, forming a basket-like structure. This structure is used to capture the sea butterfly and, once the poor shelled snail is traped, the sea angel rotates the sea butterfly’s shell until its opening is directed to the predator’s mouth.

After that, the terror begins. The poor sea butterfly has withdrawn into its shell by this time, but the sea angel uses a group of chitinous hooks in its mouth to perforate the sea butterfly’s body and, helped by the radula, pulls the whole body of the prey from inside the shell, swallowing it entirely at once. It is likely a horrible death for the poor sea butterfly. After finishing swallowing one sea butterfly, the common sea angel can go after another one in about 2 minutes.

Drawing of a common sea angel feeding on a common sea butterfly. BC = buccal cones, HK = chitinous hooks, S = the shell of the sea butterfly. Extracted from Lalli (1970).

While the life cycle of the common sea butterfly is short, lasting only a year, that of the common sea angel is much longer. As a result, there are no adult sea butterflies to serve as food for the common sea angel from later autumn to early spring. For a long time it was thought that the common sea angel would spend this whole time without eating, and indeed it was found that it can survive long periods in starvation. However, analyses of the stomach content of the common sea angel revealed the presence of amphipods and eventually calanoid copepods, suggesting that it can rely on some alternative food sources in cases of extreme necessity. Their main food, however, is the common sea butterfly with no doubt. They start to feed on them when they are still larvae, always capturing and ingesting sea butterflies that have a size similar to theirs.

Will the common sea angel be able to survive on these other prey types if the populations of the common sea butterfly decline due to climate change? If find it unlikely and I hope we don’t need reach a point in which this becomes an option.

People love to name sea creatures by making analogies with things found on land. Today’s species is one more of this type, being the best known species of the so-called sea butterflies and, therefore, known as the common sea butterfly. It has nothing to do with butterflies, though, and its scientific name, Limacina helicina, is better to describe it.

The common sea butterfly is a mollusk, more precisely a gastropod, and, as it has a shell, it is a “snail”. It does not crawl through the floor as most snails though. With a spiral shell measuring only about 10 mm in diameter, it lives in the water column and is sometimes described as a planctonic species. It can swim by itself, though, because its fleshy foot is changed into two expansions called parapodia that act as two large fins. Its shell is mostly transparent and the soft parts are mainly purple, although the parapodia are almost transparent as well.

The common sea butterfly is truly a beautiful creature, isn’t it? Photo by Russ Hopcroft, University of Alaska, Fairbanks.

The habitat of the common sea butterfly includes the cold waters of the Arctic region, including the Arctic Ocean and neighboring areas of the Atlantic and Pacific oceans. In the Pacific, it can occur southward to Japan and the northern parts of the United States. Larger specimens tend to inhabit deeper waters, up to 150 m deep, while smaller ones live closer to the surface, up to 50 m down. Until very recently, the common sea butterfly was thought to inhabit Antarctic waters as well but molecular studies revealed that the populations around Antarctica belong to a different species, Limacina antarctica.

See how fast they can beat their wings.

The diet of the common sea butterfly includes several smaller planktonic creatures, especially small crustaceans, such as nauplii (larvae) of copepods, as well as dinoflagellates, ciliates and diatoms. Juveniles of their own species are also very common, sometines making up the second most common item in their diet. In order to capture food, they produce a spherical web of mucus that floats above them in the water. This web traps other organisms in the water column and is later sucked and eaten by the sea butterfly together with the entrapped creatures. This web is very difficult to observe during the day because of diffuse refraction but appears clearly at night. When disturbed by light, however, the common sea butterfly tends to quickly swallow its web and sink to escape from danger.

A commo sea butterfly with its spherical mucous web seen as an oval concentration of finer particles right above the snail. Extracted from Gilmer & Harbinson (1986).

The thin shell of the common sea butterfly consists of aragonite, which is highly soluble and sensitive to changes in temperature and acidification of the water. Studies have shown that the expected increase in ocean acidification due to human-induced climate changes will probably have a negative impact on populations of the common sea butterfly and related species. This is particularly worrisome regarding the common sea butterfly because it is the a key species in Arctic ecosystems, being an important food source for many marine animals, such as fish, whales, birds and even other mollusks.

The little snail will not give up the fight so easily, though. Studies have shown that the periostracum (the outer organic layer of the shell) can prevent the aragonite to dissolve and an physical trauma that breaks the periostracum, allowing the direct contact of the aragonite with the water, is necessary to cause dissolution. And even when this happens, the common sea butterfly can compensate by building new aragonite layers on the inner surface of the shell and it is able to extract aragonite from water for this purpose even when the levels in water are very low.